The present invention generally relates to motor vehicles equipped with electric-type power-assisted steering. It is concerned more specifically with a device for releasing or unlocking the steering system of such a vehicle, this device intervening following previous immobilization or locking of the same steering system.
The majority of motor vehicles are equipped with a steering system immobilizing device which is actuated when the vehicle is not being used in order to serve as an antitheft device, thereby preventing the vehicle from being driven.
Immobilization of the steering system of a motor vehicle equipped with a device intended for this purpose is usually carried out manually by the user turning the steering wheel until it is in an angular position for the latching of this immobilizing device, which then produces mechanical locking of the steering column. The reverse operation of releasing the steering system in some cases requires a manual effort to be exerted on the steering wheel, without power assistance being available, so that the locking element, which is in some cases under stress, can be disengaged from its locked position. Moreover, in the case of an electric antitheft system, the driver of the vehicle may in some cases not notice that the antitheft system has remained in the locked position, which will prevent subsequent starting of the vehicle.
In order to avoid these disadvantages, document DE 10016487 A has already proposed a release device which, by taking advantage of the specific characteristics of a certain type of power-assisted steering systems, namely electric power-assisted steering systems, prevents the user from exerting a manual effort to release the steering system while eliminating the risk that starting will be prohibited, this device providing automation of the release operation. Such a steering system release device for a motor vehicle equipped with electric power-assisted steering comprises, on the one hand, a locking mechanism acting on the steering column or on another part of the steering system, and, on the other hand, in combination with the electric assist motor for the steering system, control means which receive signals from at least one vehicle status and/or initiating event detector so as to activate the electric assist motor and rotate the steering column or translationally drive or otherwise move another part of the steering system, through the action of this electric motor, until a zero torque or load or a virtually zero residual torque or load has been achieved, in return for which the locking mechanism for the steering system can be released.
Thus, when the user wishes to start the vehicle, the electric power-assisted steering system is automatically activated in order to turn the steering column or move any part of the steering system until such a value of the torque or load exerted on the steering system locking mechanism has been achieved that unlocking may take place without difficulty.
Such a device provides the results and advantages which follow:                Firstly, it offers the user the possibility of no longer having to exert manual effort to release the steering system, since the electric power assistance of this steering system is exploited to turn the steering column or move any part of the steering system until unlocking is possible, with the result that “comfort” is increased. In this respect, it will be noted that the intervention of electric power-assisted steering for such a function does not pose any problem even when the combustion engine of the vehicle is still stopped (such would not be the case for a hydraulic power-assisted steering system, which would require a pump driven by the combustion engine).        The automatic nature of the proposed device, which is equipped with “intelligence”, makes it impossible for there to be any non-unlocking of the system due to an excessively large torque or load that makes it impossible to start the engine. In fact, in all motor vehicles, whether the locking system is mechanical or electrical or other, starting of the vehicle is prohibited unless unlocking of the immobilizing system occurs.        The proposed system has a simple and economical structure. On the one hand, it can use sensors and detectors and an electronic computer which already exist on the vehicle. On the other hand, it does not require any conversion of the vehicle steering system and it uses a conventional or existing mechanism for locking the steering column or for locking another part of the steering system, this mechanism not even needing to be modified or adapted.        